Many food items such as salad dressings, e.g., French dressings and mayonnaise are prepared with vegetable oils, e.g., soybean oil. Soybean oil contains a large amount of linoleic and linolenic acids which readily react with the dissolved oxygen in the product whereby undesirable volatile compounds are produced. It has been reported that the flavour quality of oils could be improved by eliminating dissolved oxygen in the oils (for reference see Journal of Food Science 57(1), 1992, p. 196).
Antioxidants such as butylated hydroxyanisole, butylated hydroxytoluene, and propyl gallate have been added to foods containing fats to improve their oxidative stability.
Enzymatic deoxygenation with glucose oxidase has been described to reduce the amount of dissolved oxygen in salad dressings significantly (for reference see Journal of Food Science 57(1), 1992, p. 199): 0.5% glucose was sufficient to remove 92% of the dissolved oxygen in the salad dressing during 5 days of storage.
Glucose oxidase catalyzes the oxidation of d-glucose to d-gluconic acid in the presence of molecular oxygen: C.sub.6 H.sub.12 O.sub.6 +2O.sub.2 +2H.sub.2 O-&gt;2C.sub.6 H.sub.12 O.sub.7 +2H.sub.2 O.sub.2. As it can be seen a by product of this reaction is H.sub.2 O.sub.2, which can be destructive to the oil product. In order to avoid this problem it has been suggested to add a catalase together with the glucose oxidase; catalase catalyzes the reaction: 2H.sub.2 O.sub.2 -&gt;2H.sub.2 O.sub.2, but then oxygen is produced again!--however, the overall effect of the enzymatic deaeration by using a combination of glucose oxidase and a catalase is removal of 0.5 mole oxygen for each mole of oxidized d-glucose.
It is an object of the present invention to find a simple and effective enzyme system for oxygen removal in an oil or a product comprising an oil, in which hydrogen peroxide is not involved.